1. Field of the Invention
The present invention relates to a jitter measurement apparatus and a jitter measurement method for measuring an intrinsic jitter of a circuit to be tested, including a phase detector which outputs a signal according to a phase difference between a supplied first input signal and a supplied second input signal, and a phase locked loop circuit which outputs an oscillation signal synchronized with a reference clock that is supplied.
2. Description of Related Art
As a method for measuring the intrinsic jitter which is generated in an inside of a circuit, such as a Phase Locked Loop circuit, a method for detecting a jitter of the signal output from the PLL circuit by inputting a reference clock, of which jitter is enough small, to the PLL circuit is well known. According to the technology, the jitter generated in the output signal is measured as the intrinsic jitter by considering that a jitter of the reference clock has no jitter.
However, according to the conventional jitter measurement method, it is very difficult that the reference clock has completely no jitter, so that the jitter of the reference clock has inevitably an influence on the jitter generated in the PLL circuit, and consequently, it is impossible to measure the intrinsic jitter of only the PLL circuit with high accuracy. Alternatively, it is very expensive to reduce the jitter of the reference clock to be negligibly small.
Moreover, since the intrinsic jitter is calculated by measuring the output signal of the PLL circuit in the conventional method, it is impossible to specify how much the jitter is generated and which components of the PLL circuit generates the jitter.
Accordingly, it is an object of the present invention to provide a jitter measurement apparatus, a jitter measurement method, and a PLL circuit, which are capable of overcoming the above drawbacks accompanying the conventional art. The above and other objects can be achieved by combinations described in the independent claims. The dependent claims further advantageous and exemplary combinations of the present invention.